block/block-backend: blk_set_enable_write_cache is IO_CODE

blk_set_enable_write_cache() is defined as GLOBAL_STATE_CODE
but can be invoked from iothreads when handling scsi requests.
This triggers an assertion failure:

 0x00007fd6c3515ce1 in raise () from /lib/x86_64-linux-gnu/libc.so.6
 0x00007fd6c34ff537 in abort () from /lib/x86_64-linux-gnu/libc.so.6
 0x00007fd6c34ff40f in ?? () from /lib/x86_64-linux-gnu/libc.so.6
 0x00007fd6c350e662 in __assert_fail () from /lib/x86_64-linux-gnu/libc.so.6
 0x000056149e2cea03 in blk_set_enable_write_cache (wce=true, blk=0x5614a01c27f0)
   at ../src/block/block-backend.c:1949
 0x000056149e2d0a67 in blk_set_enable_write_cache (blk=0x5614a01c27f0,
   wce=<optimized out>) at ../src/block/block-backend.c:1951
 0x000056149dfe9c59 in scsi_disk_apply_mode_select (p=0x7fd6b400c00e "\004",
   page=<optimized out>, s=<optimized out>) at ../src/hw/scsi/scsi-disk.c:1520
 mode_select_pages (change=true, len=18, p=0x7fd6b400c00e "\004", r=0x7fd6b4001ff0)
   at ../src/hw/scsi/scsi-disk.c:1570
 scsi_disk_emulate_mode_select (inbuf=<optimized out>, r=0x7fd6b4001ff0) at
   ../src/hw/scsi/scsi-disk.c:1640
 scsi_disk_emulate_write_data (req=0x7fd6b4001ff0) at ../src/hw/scsi/scsi-disk.c:1934
 0x000056149e18ff16 in virtio_scsi_handle_cmd_req_submit (req=<optimized out>,
   req=<optimized out>, s=0x5614a12f16b0) at ../src/hw/scsi/virtio-scsi.c:719
 virtio_scsi_handle_cmd_vq (vq=0x7fd6bab92140, s=0x5614a12f16b0) at
   ../src/hw/scsi/virtio-scsi.c:761
 virtio_scsi_handle_cmd (vq=<optimized out>, vdev=<optimized out>) at
   ../src/hw/scsi/virtio-scsi.c:775
 virtio_scsi_handle_cmd (vdev=0x5614a12f16b0, vq=0x7fd6bab92140) at
   ../src/hw/scsi/virtio-scsi.c:765
 0x000056149e1a8aa6 in virtio_queue_notify_vq (vq=0x7fd6bab92140) at
   ../src/hw/virtio/virtio.c:2365
 0x000056149e3ccea5 in aio_dispatch_handler (ctx=ctx@entry=0x5614a01babe0,
   node=<optimized out>) at ../src/util/aio-posix.c:369
 0x000056149e3cd868 in aio_dispatch_ready_handlers (ready_list=0x7fd6c09b2680,
   ctx=0x5614a01babe0) at ../src/util/aio-posix.c:399
 aio_poll (ctx=0x5614a01babe0, blocking=blocking@entry=true) at
   ../src/util/aio-posix.c:713
 0x000056149e2a7796 in iothread_run (opaque=opaque@entry=0x56149ffde500) at
   ../src/iothread.c:67
 0x000056149e3d0859 in qemu_thread_start (args=0x7fd6c09b26f0) at
   ../src/util/qemu-thread-posix.c:504
 0x00007fd6c36b9ea7 in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
 0x00007fd6c35d9aef in clone () from /lib/x86_64-linux-gnu/libc.so.6

Changing GLOBAL_STATE_CODE in IO_CODE is allowed, since GSC callers are
allowed to call IO_CODE.

Resolves: #1272

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20221027072726.2681500-1-eesposit@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Tested-by: Antoine Damhet <antoine.damhet@shadow.tech>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -1944,7 +1944,7 @@ bool blk_enable_write_cache(BlockBackend *blk)
 
 void blk_set_enable_write_cache(BlockBackend *blk, bool wce)
 {
-    GLOBAL_STATE_CODE();
+    IO_CODE();
     blk->enable_write_cache = wce;
 }